1. Field of the Invention
The present invention relates generally to devices for cutting pipe or other cylindrical conduits. More particularly, the present invention relates to an internal pipe cutter (i.e., one which operates in the interior of the pipe) for cutting PVC pipe.
2. Description of the Prior Art
It has become quite common in the construction of both residential and commercial buildings to use polyvinyl chloride (PVC) pipe for the waste drains of the bathroom fixtures, such as the toilet, the shower, and/or the bathtub. Generally, these waste pipes are installed or roughed in before the floor of the bathroom is constructed. Thus, it is usually impossible when the pipes are first installed to accurately measure the length of pipe needed. Consequently, the pipes must later be cut to the proper length after the floor is installed; usually, it is required that this cut be at or below the level of the floor to allow proper installation of the bathroom fixtures. This "below grade" cutting presents certain problems since the pipe obviously cannot be cut by a saw or other tool which is operable on the external surface of the pipe.
A number of prior art devices, generically known as internal pipe cutters, have been proposed for cutting PVC pipe as well as other types of pipe from the interior thereof. However, these prior art pipe cutters all exhibit various disadvantages. For example, U.S. Pat. No. 3,999,292 to Breese discloses an internal pipe cutter having a cutting drum which slidably mounts a cutting bit therein. The cutting bit is urged outwardly into engagement with the pipe by a plurality of springs contained in a recess in the cutting drum. However, as the springs force the cutting bit outwardly, they simultaneously force the remainder of the cutting drum rearwardly into engagement with that portion of the pipe opposite to the portion contacted by the cutting bit. When these springs are strong, the cutting drum may be engaged with the pipe with a great deal of force. Thus, as the cutting drum is rotated to cut the pipe, the friction between the drum and the pipe gradually heats the pipe. In some instances, this frictional heat is so great that it can melt or deform the pipe. This requires that the damaged pipe be removed and replaced which is a laborious and time consuming procedure.
Other internal pipe cutters are known which do not utilize springs for forcing a cutting bit outwardly. For example, U.S. Pat. No. 3,911,574 to Jones discloses the use of centrifugal force to throw the cutting bit radially outwardly. U.S. Pat. No. 3,883,950 to Kurtz discloses the use of a movable wedge to cam the cutter bits outwardly into engagement with the pipe. In this latter type of cutter, springs are often used to keep the cutter bits normally retracted until forced outwardly by the wedge.
In those devices which utilize a movable wedge or cam (e.g., Kurtz), the wedge must be actuated to move the cutting bits outwardly before the cutter can be rotated to cut the pipe. In addition, when cutting relatively thick pipe, the cutter may have to be stopped a number of times to readjust the cutter bits to maintain contact with the pipe. With regard to the centrifugally operated cutter shown in Jones, although the rotating movement of the pipe cutter moves the cutter bits radially outwardly, these bits are not enclosed in any type of guide drum. Therefore, in some instances, the bits might be susceptible to jamming by the pipe fragments broken off of the pipe by the cutter bits.
Finally, most prior art internal pipe cutters are difficult to remove if they become jammed inside the pipe without actually physically breaking the floor and pipe apart to remove the cutter or trying to dismantle the cutter from outside the pipe. For example, in cutters which disclose the cutting bit as being enclosed inside a cutting drum, no provision is usally made for easily disengaging the cutter bit if it should become jammed. When the cutting bit of an internal pipe cutter becomes jammed, it has been the usual practice to break away the floor surrounding the pipe to free the cutter. Such an operation requires that a new section of the pipe be installed and that the floor be rebuilt around the pipe as necessary. The extra expense and labor entailed bythis procedure is apparent.